Ammonium Dichromate

How Do You Define The Terminology Ammonium Dichromate(NH4)2Cr2O7?

Ammonium dichromate is an inorganic compound with the chemical formula (NH4)2Cr2O7. It is orange-red needles produced during crystallization.

Ammonium dichromate is a salt consisting of ammonium ions and dichromate ions, a toxic chemical salt used to sensitize organic emulsion. It is more sensitive to light.  It is readily ignited and burns to leave a sizable green residue. If ammonium dichromate is heated in a closed container, it may rupture due to the decomposition of the material. It also acts as a reliable oxidizing agent mixed with or contaminated with combustible material.

The following figure highlights a few of the things about Ammonium dichromate:

Because of its application in demonstrations of tabletop "volcanoes", Ammonium dichromate is sometimes also termed as Vesuvian Fire. However, in schools, this demonstration became unpopular due to the compound's carcinogenic nature. It has also been used in pyrotechnics and the early days of photography.

A glimpse, let's have a look to the names of Ammonium dichromate:

IUPAC name – diammonium oxido-(oxido-dioxo-chromio) oxy-dioxo-chromium,  

Other names – Ammonium bichromate 

Ammonium pyrochromate, Chromic acid, diammonium salt; diammonium dichromate; Ammonium bichromate; Ammonium pyrochromate.

The following points and table give a depth-understanding of the various features or characteristics of Ammonium dichromate. These are as follows:

  • The density of ammonium dichromate is 2.12g/cm 3

  • It has a melting point of 180°c

  • Exact molecular mass -   251.924166

  • Ammonium dichromate is an explosive compound.

  • The action makes chromic acid on ammonium hydroxide with subsequent crystallization. 

Features of Ammonium Dichromate

H8Cr2N2O7

Ammonium Dichromate

Density

2.12 g/cm³

Molecular Weight/ Molar Mass

252.07 g/mol

Solubility in water

18.2g/100ml (0°c)

40g/100ml(20°c)

156/100ml(100°c)

Autoignition temperature

190 °C

Melting point

180 °C

Chemical Formula

(NH4)2Cr2O7


Ammonium Dichromate Structure – (NH4)2Cr2O7.

The Ammonium dichromate follows a particular pattern or structure. This can be seen as follows: 

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Properties of Ammonium Dichromate

The properties of Ammonium dichromate are explained by dividing them into two main categories. These are:

  1. Physical Properties.

  2. Chemical Properties.

These will be explained one by one as follows:

Physical Properties of Ammonium Dichromate – (NH4)2Cr2O7

The physical properties of Ammonium dichromate are as follows:

  • It is orange-red crystals.

  • It is soluble in water and alcohol at room temperature.

  • Ammonium dichromate is odorless.

Other Properties Can Be Made More Transparent With The Help of The Following Chart

Odor

Odorless

Appearance

Orange-red crystals

Stability

Stable under recommended storage conditions

Specific Gravity

2.1500

Solubility

Insoluble in acetone, soluble in alcohol.

Chemical properties of Ammonium Dichromate-

At room temperature and pressure, it is orange, acidic crystal soluble in water and alcohol. On heating Ammonium dichromate, it undergoes decomposition, resulting in chromium (III) oxide and nitrogen gas formation.

(NH4)2Cr2O7(s) → Cr2O3(s) + N2 (g) + 4H2O (g).

 Hazards and safety of Ammonium Dichromate -

Main hazards of ammonium dichromate are as follows:

Dangerous, very toxic, a carcinogen, mutagen, oxidizing, dangerous for the environment.

To deal with these hazards, one needs to follow safety measures. These includes:

Safety: Ammonium dichromate, like all chromium (VI) compounds, is highly toxic and is also explosive under certain conditions. It is also a strong irritant.

Safety measures need to be taken while using ammonium dichromate. Wear eye protection and avoid skin contact with ammonium dichromate (wear gloves).  

Uses of Ammonium Dichromate – (NH4)2Cr2O7

Ammonium dichromate has various applications. These are explained as follows:

  • Ammonium dichromate is used in sensitizing solutions used in lithography.

  • They are used in pyrotechnics, lithography, and photoengraving. It is also used as a magnetic recording material.

  • It is used as an approved pesticide and used as a mordant for dyeing, used as a pigment.

  • It is also used as a mordant for dyeing pigments, in the manufacturing of alizarin, chrome alum, leather tanning, and oil purification. 

Reactions: Ammonium dichromate depicts various reactions, and these include:  

Oxidation Reactions

Ammonium dichromate acts as an oxidizing agent. Often reacts violently with any reducing agent: the more influential the reducing agent, the more violent the reaction. Even in the oxidation of aliphatic alcohols, the compound is being applied. This is being used for their corresponding aldehydes and ketones in ZrCl4/wet SiO2 in solvent-free conditions. This is done again with relatively high yields.  

Reactions: Consisting of tabletop volcanoes and thermal decomposition.

If you add a few drops of ethanol to a small pile of ammonium dichromate and ignite, you will notice a spark will emit, and an ash-like product will form. This phenomenon resembles the eruption of a volcano.

FAQ (Frequently Asked Questions)

1. What Happens When Ammonium Dichromate is Heated?

When it is heated, Ammonium dichromate (NH4)2Cr2O7 decomposes to produce chromium (III) oxide Cr2O3, nitrogen gas, and water vapor:

(NH4)2Cr2O7 (s) → Cr2O3 (s) + N2 (g) + 4H2O (g)

This reaction is based on a standard demonstration known as the "ammonium dichromate volcano."

Orange-red color crystalline solid on intense heating swells up & decomposes violently with flashes of light. Greenish residue also gives steamy dunes, which condenses cooler parts of the test tube to form tiny droplets of water. 

(Water is gaseous in this reaction due to the relatively high reaction temperature), and stable chromium (III) oxide. 

As compared to the original ammonium dichromate, chromium (III) oxide crystals are "fluffier.” 

Much of the mass of the starting material getaway as nitrogen gas and water vapor, the result looks like a much more significant amount of substance.


2. What are The Uses of Ammonium Dichromate?

Ammonium dichromate has been used in pyrotechnics and also plays an essential role in the early days of photography as well as in lithography, as a source of pure nitrogen in the laboratory, and as a catalyst. 

It is also used as a mordant for dyeing pigments, in the manufacturing of alizarin, chrome alum, leather tanning, and oil purification.

Photosensitive films containing PVA, ammonium dichromate, and a phosphor are spin-coated as liquid slurries in the production of the phosphor raster of the TV screens, LCDs, and many other different devices. On the other hand, the ammonium dichromate acts as the photoactive site as well.